The present invention generally relates to the production of articles of manufacture in a computer simulation or in the real world, and more particularly, to a method for accurately evaluating pattern compliance for a simulated or manufactured article.
American, Canadian, German, and International Organization for Standardization (ISO) standards define methods for specifying multiple levels of pattern and feature related tolerances often referred to as composite positional tolerances. Composite positional tolerances include a pattern locating tolerance and a feature relating tolerance. A pattern locating tolerance is a tolerance that relates a collection of manufactured features on an object relative individually to the specified datums of the designed pattern. A feature relating tolerance can include a tolerance relating to the size of a feature, the positions of a set of features relative to each other, and the rotation of a pattern of features relative to a specified origin.
Another specification may include maximum material condition (MMC) and least material condition (LMC). MMC may be defined as the condition in which a feature of size contains the maximum amount of material within the stated limits of size, for example, minimum hole diameter or maximum shaft diameter. LMC may be defined as the condition in which a feature of size contains the least amount of material within the stated limits of size, for example, maximum hole diameter, or minimum shaft diameter. An allowable tolerance may be specified as the combination of the pattern-locating and feature related tolerances and a material condition.
Presently, the manufacturing industry does not have an efficient or effective way of determining whether or not the feature relating requirements are achieved. Inspection of manufactured articles and analyzing the resulting data are not currently evaluated in an automated and correct manner to determine whether or not combined manufactured features such as hole size and location are acceptable to the applied feature relating tolerances. For example, evaluating manufactured hole size, form, orientation, and location are all completed separately, and confidence in the accuracy of each evaluation is low.
Referring to FIG. 1, one method for documenting inspection data consists of paper gaging, where information is recorded on paper. Measurements are taken, and hole positions 92 are plotted on a grid 94 at an enlarged scale using a true position 96 as the origin. Concentric circles 90 representing tolerance zone diameters are then overlain to determine compliance with the pattern locating tolerance. This method does not consider variation in feature size easily, and does nothing to examine compliance with the feature relating tolerance.
As can be seen, there is a need for accurately determining inspection data. Also, there is a need for determining inspection data in a timely manner, with perhaps, using only a single iteration. Moreover, there is a need for quickly analyzing inspection data in a step of the manufacturing process so that the results of the analysis can be used in subsequent processes.
Variation effects within a pattern of features may also be determined when performing a variation analysis of a design prior to manufacturing that design. The variation analysis software performs hundreds or thousands of simulated build cycles, and in each cycle, varies all of the parameters randomly. Assembly variation analysis that utilizes feature patterns, such as holes, for assembly is currently reliant on approximations and iterations for the assembly of parts. Such a process may introduce error, is inefficient, and requires advanced software skills for completion.
In addition to the need for assessing produced parts, there is a need to accurately determine the variation effects on patterns of features during variation analysis.